We utilize a social ecological model to understand longitudinal changes in HIV risk and prevention behaviors among chronically homeless, predominantly African American men and women who transition into permanent supportive housing (PSH). Homeless persons face disproportionate risk of HIV and drug use. PSH is intended as the locus of integrated health services for this vulnerable population, yet there has been almost no research to understand HIV risk and prevention among residents, or the provision of HIV prevention services within PSH, except specifically for people living with HIV/AIDS. Some evidence suggests that transitioning to housing could increase rather than decrease risk behaviors over time, although research to clarify these complexities is absent. Specific Aims are as follows: 1) To examine how transition to PSH is associated with HIV risk and prevention behaviors over time; 2) To examine how transition to PSH is associated with changes in social networks of PSH residents, and how networks are associated with changes in HIV risk and prevention behaviors over time; 3) To examine how transition to PSH is associated with changes in drug use and mental health symptoms among PSH residents, and how changes in these individual characteristics are associated with HIV risk and prevention behaviors over time; 4) To determine whether and how PSH providers promote HIV prevention, and to understand policies and procedures that may impact HIV risk among residents; 5) To synthesize findings from Aims 1- 4 to inform specific strategies to reduce risk of HIV transmission and to enhance HIV prevention services for residents in PSH. Aims 1-3 will be addressed through structured interviews (baseline, 3, 6, 12 months) with consecutive admissions to PSH (N=405 at 12 months). Aim 4 will be addressed through individual interviews with supervisory staff (N=30) and focus groups with front line staff (N=100) of PSH programs, and ethnographic shadowing of PSH residents (N=30). Aim 5 will synthesize findings of Aims 1-4 through focus groups with 50 PSH providers and 50 residents.